The invention concerns a method of producing passivated urea or urea based compounds for fertilizer blends wherein the urea particles are treated with a mineral acid that reacts with urea and creates a grasping layer. Thereafter a solid base in powder form is added in excess to the particles to coat the acidified particle surface. The invention also concerns a fertilizer blend comprising the passivated urea or urea based compounds with one or more of AN or AN-based compound, NS products, superphosphates, and more generally with a priori most compounds that urea is susceptible to react with when in direct contact. A safe blend comprises more than 40 weight % of the passivated urea.